The present invention relates to a battery block comprising at least two battery packs, and to a method for manufacturing a battery block.
Battery blocks are used in various electrically powered devices, in particular in electric vehicles, in electrically driven bicycles, in battery-powered tools, or portable battery cases. Typically, multiple battery packs are used in such battery blocks, wherein each battery pack comprises several battery cells. Rechargeable battery cells, in particular lithium-based rechargeable battery cells, are frequently used in such battery packs of which the battery block is made up. However, the invention is neither limited to rechargeable battery cells, nor to lithium-based battery cells and may be implemented in any way. Rechargeable batteries or accumulators are characterized in that they may be recharged again after a first discharge process. However, this requires an appropriate control of the charging and discharging process, by a battery management system, for example.
When using multiple battery cells within a battery pack and combining multiple battery packs in a battery block, it is very important to form the electrical connections between the individual battery cells and the battery pack and between the individual battery packs in a reliable manner. These different electrical connections must function reliably both during operation of the electrical device, i.e., under corresponding mechanical, thermal and electrical stresses, and throughout the life span of the electrical device. When using multiple battery packs in one battery block, which can thus comprise several hundred battery cells, large currents occur during charging and discharging, which flow, when interconnecting multiple battery packs, in particular at the connection regions. Where large currents flow, a lot of heat is also generated, the uncontrolled transfer of which to the battery cells must be avoided, since battery cells, in particular lithium-based cells, can outgas or even explode in case of uncontrolled addition of heat.
Thus, in the prior art, various technologies are used in order to prevent an excessive influence of heat on the battery cells both during assembly of the battery pack and during the charging and discharging process. One approach for preventing an excessive thermal stress of battery packs and the battery cells within a battery pack consists in constructing the spatial dimensions of the battery pack in a liberal manner, such that sufficiently great distances between the individual battery cells exist. In a similar manner, when interconnecting multiple battery packs to a battery block, cables between the individual battery packs are used in order to interconnect these battery packs. The permanent need for reducing the size of electrical devices, in order to have more storage space or a bigger passenger cabin in an electrical vehicle, speaks against a more liberal spacious partitioning with more volume. Thus, there exist many efforts to compress the interconnection of battery cells in battery packs and the interconnection of multiple battery packs to battery blocks as much as possible, such that very many cells can be installed in a minimal volume. A further aspect of the design of battery blocks being assembled from at least two battery cells is that individual battery cells among the many battery cells within one battery pack may fail during operational life due to inhomogeneities within the cells, wherein the failure is caused by a low internal resistance and thus results in an increased current flow at the connection structures of the battery packs and at the connection regions of the battery block. This increased current flow may result in an uncontrolled heat generation in the cell and also in the neighboring cells, which can also lead to a chain reaction, such that the whole battery pack outgases in an uncontrollable manner or explodes. To avoid such effects, it is necessary to design the battery packs being interconnected to a battery block such that they are simple to produce and have a reliable electrical contact by their corresponding design both during operation and for withstanding the mechanical and thermal stresses. Further, the battery block with the several battery packs should have a space optimized arrangement which allows for flowing of very large currents without leading to a thermal overload of the individual cells.
At the same time, the failure of an individual cell must not lead to the failure of the battery pack or the battery block. Further, the replacement of defect battery packs or battery cells should generally be enabled.